1. Field of the Invention
The present invention relates to a shaping apparatus of the type using a liquid forming medium. More particularly, it concerns shaping apparatus in which a workpiece to be formed is pressed by a solid upper die or punch on one side and is retained against the upper die by liquid contained on the other side of the workpiece.
2. Description of the Related Art
A shaping apparatus of the type using a liquid workpiece shaping medium is known and shown, for example, in Japanese Utility Model Publication SHO 61-97322. In FIG. 3 of the accompanying drawings, such a shaping apparatus includes a lower clamp 32 and an upper clamp 34 for clamping a workpiece W' therebetween, an upper die or punch 36 movable relative to the workpiece W' to deform the workpiece W' when lowered, and a pressure well 38 disposed below the lower clamp 32 as a separate component. The pressure well 38 defines a cavity 42 of large volume and in communication with a liquid flow passage 44 for respectively supplying and draining liquid F to and from the cavity 42. A well insert 40 may be inserted into the cavity 42 to reduce the inside diameter as well as the volume of the cavity 42.
In operation, the workpiece W' is peripherally clamped between the lower clamp 32 and the upper clamp 34. Then, the punch 36 is lowered to deform the workpiece W' against the liquid F' in the pressure well 38. The liquid constrains the workpiece W' against the punch 36 and acts to shape or conform the workpiece W' to the configuration of the lower surface of the punch 36.
However, there are the following problems in the conventional shaping apparatus of FIG. 3:
First, in the case where an upper surface 32a of the lower clamp 32 undulates in a peripheral direction between an elevated crest shown in cross section in FIG. 4 and a depressed valley shown in elevation on the center line of the lower clamp in FIG. 4, a liquid level cannot be set above a lowermost portion of the undulating upper surface 32a of the lower clamp 32. Air in a space V' below the elevated crest portions of the undulating surface 32a and the liquid surface results in air pocket while the workpiece W' is being press-formed. Though air in the air pocket is compressed and a volume of the air pocket is decreased during the work piece shaping operation, a relatively large volume of the air pocket still remains. The result is that a portion of the workpiece contacting the air pocket tends to acquire an undesirable fold deformation or wrinkle, and the visual quality of the workpiece is degraded.
Second, the liquid in the well 38 acts against the lower clamp 32 not only in a horizontal direction with a side pressure P1 but also in a vertical direction with a vertical pressure P2. Therefore, because the lower clamp 32 should be supported so as to be able to endure these pressure loads, the apparatus is large in size and of increased cost.
Third, since the volume of the cavity 42 in the pressure well 38 is large, for example, about 4,000 liters, it takes a relatively long period of time to supply and drain liquid to and from the cavity 42, and this makes it difficult to improve work efficiency.
Fourth, when the well insert 40 must be used for the purpose of decreasing the actual volume of the cavity, it has been found to be a difficult task both to put the well insert into the well and to remove the well insert from the well. Further, the well insert 40 requires an increase in the number of required parts and a resulting increase in cost.